10-22 is the widest rectilinear lens you can get, AFAIK, so if you want that true UWA coverage without something like the 8-15 or a prime 8mm fisheye, then it's a great lens, and will get you 16mm FF equivalent, which is pretty darn wide.
The widest I have is the 17-55, which I have been very happy with, and which is wide enough for me. Even if you get the 10-22, there's so little overlap in focal length, I'd say you should consider the following: 17-40 or 17-55 for general purpose first, and then 10-22 for wide angle if you find 17 on crop isn't wide enough.
EF 17-40 f/4L vs EF-S 17-55 f/2.8 IS L :
advantages of 17-40:
FF compatible, should you go that way in the future
advantages of 17-55:
longer on the tele end
2.8 max aperture
for me, I decided the 2.8 max aperture and additional 15mm of range were worth the cost. IS wasn't super important, but is nice to have. I have no intention of going FF (my next body will be a 7d2 whenever that comes out... for now I'm sticking with my 7d.) You just have to ask yourself what you want/need, and which is more appropriate. Or neither, really- who am I to tell you what to consider.
Just my two cents.